Canon Color Bubble Jet BJC-1000 Series User Manual page 42

Prepare the
envelopes.
Chapter 3
Arrange the stack of envelopes on a firm surface and press
down firmly on the edges to make the folds crisp.
Press all the way around the envelopes to remove any
curls and expel air from inside the envelopes.
Make sure any curls are removed from the flap of each
envelope.
Make sure the flaps are straight. Use the end of a pen or
similar object to flatten the leading edge of envelopes.
PRESS DOWN FIRMLY ON
THE EDGES OF THE FLAP
Paper Handling 3-13